1. Field of the Invention
The present invention relates to a vehicle dynamics control device that controls the braking force and the driving force imparted to each wheel so as to achieve an optimal state of vehicle dynamics.
2. Description of Related Art
There are devices known in the related art that slow the subject vehicle so as to achieve an optimal speed for avoiding a collision with an obstacle present ahead of the subject vehicle or for traveling along a curve ahead of the subject vehicle through an automatic downshift or an automatic brake engagement in correspondence to the particular obstacle or curve (see, for instance, Japanese Laid Open Patent Publication No. H6-36187 and Japanese Laid Open Patent Publication No. H10-269499). While such a device calculates the required deceleration and slows the vehicle based on information indicating details of the obstacle, the curve or the like present ahead, there is a concern that the wheels may skid to an excessive extent due to the automatic deceleration under certain conditions including a condition in which the friction coefficient of the road surface is low.
In addition, when regenerative braking control is executed in an electric car or a hybrid electric vehicle traveling on a road with a low coefficient of friction, deceleration control may cause the wheels to skid to an excessive extent. In particular, as control is executed to apply a greater braking force to the rear wheels than to the front wheels in an electric car equipped with an electric motor installed at the rear wheels in order to regenerate a greater amount of energy at the rear wheels, the rear wheels may skid to an excessive extent to compromise the stability of the vehicle dynamics.
Methods that have been proposed as means for addressing these issues include a method whereby the automatic deceleration control is terminated upon detecting excessive skidding of the wheels, a method whereby deceleration control is executed by engaging an antilock braking system for preventing the wheels from locking up and a method whereby the risk of a skid is estimated based upon the temperature, the state of wear of the tires or the condition of the driver, and the deceleration to be achieved is corrected accordingly (see, for instance, Japanese Laid Open Patent Publication No. H6-1229 and Japanese Laid Open Patent Publication No. 2007-216839).